This benchmark checks comparison with StringAt functions against
each other and and constants. The benchmarks will serve to measure
the effect of an optimization that will omit the implicit
String.fromCharCode in such cases.

Bug: v8:7531
Change-Id: I171df92301516c96beb6a4ed86f1dec8d10e34f5
Reviewed-on: https://chromium-review.googlesource.com/957086Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51839}